Slurry type blasting agents



United States Patent 3,282,752 SLURRY TYPE BLASTING AGENTS Robert B.Clay, Bountiful, and William N. Bryan, Salt Lake City, Utah, assiguorsto lntermountain Research and Engineering Company, a corporation of UtahNo Drawing. Filed Sept. 21, 1965, Ser. No. 489,052 17 Claims. (Cl.149-22) This invention relates to an improved slurry type blasting agentcomprising inorganic nitrates and a sensitizing agent. It relates moreparticularly to an aqueous gel or slurry in which certain ingredientsare not dissolved and which is thickened in sucha manner as to hold theundissolved constituents in suspension.

In recent years the use of ammonium nitrate aqueous gels or slurries forhard rock blasting and analogous purposes has increased rapidly.Ammonium nitrate, particularly when wet or in an aqueous slurry or gelis practically impossible to detonate unless it is sensitized. Variousmaterials have been proposed for such sensitization,

including granular TNT, finely divided metals, particu-- larly aluminum,and combinations of these and other in gredients. Examples are U.S.Patents 2,930,685 and Reissue 25,695. In general, reference to inorganicnitrates herein includes sodium nitrate, which in some respects atleast, is an equivalent for ammonium nitrate and fre- Y I quently can beand is substituted in part therefor.

The sensitizing materials, mentioned above, especially the heatproducing metals and metalloids, such as magnesium, ferro-silicon,ferro-phosphorus, some of the boron compounds, and particularlyaluminum, in particulate form, when properly used, are effective fortheir purposes provided that they can be kept properly distributedthroughout the blasting agent until it is set off. Because theundissolved particles, e.g. of aluminum and other metals, and also ofexplosive sensitizer materials and thickeners have been used, such asguar gum, and

flour, starch, etc. One object of the present invention is to makeimprovements in the thickening or gelling aspect of the explosivecomposition.

Another problem which has been encountered in the prior art is that ofproducing an explosive composition which is safe over the temperatureranges encountered in preparation, handling and use and which also hasthe necessary sensitivity at the time and conditions of detonation.Generally speaking, slurry or gel explosives, particularly those wherewater is present in any quantity, have a steep temperature-sensitivitygradient. At high temperatures they are undesirably sensitive, or, ifmade insensitive for high temperature safety, at low temperatures theyare so insensitive that it is difficult to insure detonation, even withpowerful boosters and detonators. Another object of this invention is tochange this gradient so that the compositions are sensitive enough overa fairly wide range of temperature that they can be detonated withboosters and detonating devices of reasonable size and cost while at thesame time being safe for handling over the entire temperature range,including an elevated temperature range at which they may be mixedoriginally.

Ammonium nitrate, alone or in an aqueous solution,

is normally quite insensitive and hence can be shipped and handledwithout danger, even at elevated temperatures. But ammonium nitrate isnot sufliciently soluble at low or common ambient temperatures to beincorporated in some of the aqueous solutions that are otherwisedesirable in sufficient proportions for good blasting compositions. Forthis reason, it is desirable to have in the finished explosive aconcentrated solution of this material or its equivalent, e.g. of 2 to 3or more parts by weight for each part of liquid. When the liquid iswater, this requires a fairly high temperature. than Water, such asalcohols, lower amidies, ethylene glycol, and aqueous solutions thereof,for example, it is even less soluble. In practice therefore, a solutionis often made up at a temperature of at least C., and it may be as highas 75 C. or more. Sensitizers and other undissolved or insolublematerials are not added to this hot solution until the latest convenienttime but they must be added before the material is placed in theblasting hole or site. The insolubles, which include the sensitizers,such as particulate aluminum and/or TNT, a thickener, often a fuel,etc., are often in the form of a premix. A particularly desirable methodof placing gel or slurry explosives in bore holes is to mix them at thesite and pump them directly into the hole. As soon as the sensitizermaterial is added to the solution to form a slurry, the blasting agentis hazardousto a considerably greater degree. According to one aspect ofthe present invention, however, the hazard is minimized by so preparingthe composition that it is only moderately more sensitive at thesolution temperature than at the temperature of use, which is oftenconsiderably lower.

It has been discovered, according to the present invention, that thetemperature-sensitivity gradient of a sensitized inorganic nitrateblasting slurry can be made considerably flatter thanit is normally, byincorporating substantial quantities of both sulfur andsodium nitratebut within narrower and lower ratio limits than was heretofore deemeddesirable. By this means a composition which might otherwise be toosensitive for safety at an elevated mixing temperature, or if made lesssensitive kind may be so sensitive at a mix-ing temperature of, say,

C., as to be hazardous and still be too insensitive for detonation whenin place for blasting at a temperature of 10 or 15 C.

It has been suggested in the past that a combination of ammoniumnitrate, sodium nitrate, water, and sulfur, to-

Patented Nov. 1, 1966- For liquids other 3 The theoretical optimumweight ratio of sodium nitrate to sulfur should be about 5.3, assumingthat all the sulfur reacts to form Na SO Using ratios of around 1:1 ofNaNO to sulfur, by

4 fiattest form at a SN /S ratio of around 1.2. Very satisfactoryperformance is shown at a ratio within the range of about 1 to 1.6 and agood useful range can be as low as 0.8 and up to about 3.0.

weight, it was found that sensitivity of the slurry in- 5 In acomposition using more sodium nitrate and relacreased but that thetem-perature-sensitivity relationship tively less ammonium nitrate, thesame trend was found. ch-anged drastically. With a slurry made up ofabout At low sulfur contents, these products were quite insensi- 80 to90% of aqueous solution containing several times tive, even at 60 C. Assulfur was increased, other comas much ammonium nitrate as a sodiumnitrate, and a ponents being held relatively constant, sensitivityinsolids premix of aluminum powder, sulfur, powdered 10 creased up tothe point where the sulfur almost equalled gilsonite (added as a fuel)and a finely ground guar gum the sodium nitrate, then declined. The sameflattening (as a thickener), proportions of sulfur were varied rather ofthe temperature sensitivity gradient was observed. Rewidely. Results areshown in Table I. sults are given in Table 11:

TABLE II Mix No Parts Gil S SN SN/S 60 C., 40 0., Results, 60 0.Results, 40

Soln. g./cm. gJem. C.

82.8 6.5 20.2 1.34 1.38 3F, 4F, F1 6F. 79.8 4.5 5 19.7 3.9 1.34 1. 40 415, SE, 6F bottom- 76.8 2.5 19.2 1.9 1.34 1.38 21 1, 2 41) 4F5, 5D, 6D.73.8 0.5 15 18.7 1.2 1.35 1.39 2D 4D, 5D. 69.3 0 18.1 0.9 1.35 1 39 21%,2, D 4D, 51).

TABLE SULFUR CONTENT ON 25 In the mixes of Tables II, the solution had acomposi- SENSITIVITY o tron of 52.8% AN (ammomum nitrate), 13.0% SN,Thefitandard formula employed a 70 solutlon Wlth 15.9% water and 0.1% ofthe phosphate inhibitor. Of lngredlems as follows: the dry ingredients,the guar gum thickener contributed Sol 7 Dry 1.5%, the coarser aluminum1.9% and the fine aluminum 0.3% by weight. Sulfur and SN were added toAN SN Hi0 Gum MA MB Gil S make up the various mixes in proportionsshown-Mix No. 11, with no sulfur, failed even in a 5-inch column 59A 13A159 (L1 L5 L9 as L5 30 at 60 C. as did Mix No. 10 also, with 5% sulfur.The results changed dramatically when the sulfur began to This mixcontains 88.8 solution and 11.2 parts drys. aPPfOaCh ProPomons thesQdlum For test variation the quantities of gum and aluminum Sincesulfur and sodium nitrate are widely available were held fixed. Theappropriate columns indicate the fl 10W f h may P Substantial qpercentages sodium nitrate, sulfur, gilsonite, ratio of the tltles toobtain sensitive composltions which perform well total SN to S contentand the number of parts of the 4" at moderately low temperatures and arestill safe at higher identical solution that was used in the standardformula. temperatures.

Mix No. Parts Gil 8 SN SN/S 60 0., pC., Results, Results, 40

Soln. glam. gJ mfi C. C.

90.0 5.3 1.0 13.7 13.7 1.29 1.36 2D 6F". 90.0 5.3 1.0 13.7 13.7 1.301.35 2F, 2%D 41%, 51 6F9. 88.8 4.5 3.0 13.4 4.5 1.30 1.35 2F 4D 6F. 87.53.8 5.0 13.2 2.6 1.30 1.35 D 86.2 3.1 7.0 13.0 1.9 1.31 1.39 D 84.9 2.49.0 12.9 1.4 1.34 1.37 83.7 1.6 11.0 13.6 1.1 1.34 1.40 81.3 0 15.0 12.30.8 1.35 1.39 87.3 0 9.0 13.2 1.5 1.37 1.40

l The length to diameter ratio for all charges was 6.

' No'ns.6Fnetc. signifies 6" dis. charge tailed leaving about 12olslurry. 5D etc. signifies 5' dia. charge detonated leaving a crater.

It will be noted that the products in the first three mixes failed todetonate in 5 and 6-inch columns at 40 C. but detonated in 2, 2 /2 and4-inch columns, respectively, at 60 C. This represents a largediiference in sensitivity. By contrast, the composition of Mix No. 5failed at 60 C. in a 2 /2 inch column, fired in a 3-inch column, andalso fired at 40 in a 5-inch column while failing in a 4-inch. Thesensitivity-temperature gradient here is much flatter than in the firstthree mixes.

Also, it will be noted that Mix No. 8, having the lowest SN/S ratio ofall, detonated readily at 60 C. in a 2-inch column. It failed in a4-inch, but detonated in a 5-inch column at 40 C., showing a slightlysteeper gradient than Mix No. 5. Mix No. 9, a relatively insensitive onefailed at 60 C. in a 4-inch but fired in a 5-inch column. It failed at40 C. in a 6-inch column. The reason for the insensitivity ofMix No. 9is undoubtedly its large positive oxygen balance. From these data, itclearly appears that the temperature sensitivity gradient reaches its Inlieu of the ammonium nitrate, chlorates and perchlorates may be used, atleast in part, with similar results.

Another series of experiments were made, using constant proportions ofsulfur and varying the sodium nitrate. Here it was found thatsensitivity dropped as the SN content was lowered, especiallysensitivity at lower temperature. This confirmed the observations abovethat optimum temperature-sensitivity performance is obtained when theSN-sulfur ratio is in the neighborhood of about 2.5:1 to 111. Too low aratio is as bad or worse than a ratio that is too high.

In these experiments a standard procedure w-as followed, employing a 70C. solution made up of 45.1% 'AN, 16.5% H 0, 20% SN (this ingredient wasvaried) and holding the coated aluminum at 2.0%, the fine at 0.2%, thegum at 1.2% and sulfur at 15%. Results are shown in Table III.

Maca

To check the blasting potential of mixes made according to thisinvention, a series of seismic tests were made.

Sensitivity and seismic strength do not necessarily coordinate. As abasis of comparison, some mixes of the following composition were madeup and sulfur content 1 The PS refers to potato starch.

The sulfur content does not substantially affect seismic strength.

Starch thickeners have been used in the past in connecfact that thesolution temperature for the potato starch was 70 C. while for guar gumit was 45 C. Other factors being equal, the lower the permissible miXtemperature,-the more sensitive the slurry can be made at the boreholetemperature, as a general rule. 7 v

The use of starches as thickeners is limited, however, by the fact thatthey will hydrate only at elevated tom'- peratures. Raw potato starchfor example, will not thicken satisfactorily below about 58 C. Thischaracteristic of starches may somewhat limit their application when theborehole temperatures are relatively low. Tapioca flour will hydrate ata temperature a few degrees lower than potato starch; hence it can beused in lieu thereof with advantage in some cases. However, the tapiocaflour requires a little more fine aluminum as sensitizer for equivalentresults. Table 5 shows a comparison of some sodium nitrate-sulfurcontaining slurries sensitized'with small proportions of fine aluminum,using various thickeners. In the first series a natural gum thickener(gmar gum) was employed, whereas in the second potato starch was used asthickener. The solutions were somewhat different because the first groupwere mixed at 41 C., with a 45 solution temperature, whereas the secondwas mixed at 56 C, with a 70 solution tion with slurry explosives of thesame general type to temperature.

TABLE v I Results Mix No. Coarse Fine S Gum AN Density, (g./cm.=)

Al Al 41 0. 25 0. 41 C. 25 c 1.0 0.2 6 1.2 6 1.30 1.37 Not capsensitive- 6Fw 0.8 0.4 6 1.2 6 1 31 1.39 do 61% 0.2 0.4 a 1.2 7 127 1.35do 6F1 0.6 0.6 6 1.2 7 1 29 1 36 Some reaction 6D 0.8 6 1.2 7 1.28 1 36,3F2 with Cap 6D Results Mix N0. Coarse Fine Gil. S P.S Density, (gjcmfi)Al Al 25 0.

9 1.0 0.2 4 4.5 a 1. 32 1. 40 Some reaction 5 left bottom 15 1.0 0.2 45.0 2.5 1.25 1.34 do 6D which this invention relates. In connection withthe In the first group the solution comprised 48.9% of particularingredients which characterize the composition ammonium nitrate, 15.5%of sodium nitrate, 17.1% of of the present invention, however, they havesome desirwater, and 0.1% of the aluminum-water reaction inhibiableproperties that are unusual. For example, about 3% tor, the solutionbeing made up at 45 C. The overall of starch is needed to be equivalentin thickening power mix, with dry ingredients added, had a temperatureof to 1% of guar; however, the price of starch is so much 41 C. In thesecond case thesolution was made up at less that the economic differencefrequently favors starch. 70 C. and consisted of 58.4% of ammoniumnitrate, Moreover, starches thicken more rapidly than gums, a 13.3%sodium nitrate, 15.5% water, and 0.1% of the feature which makes themmore desirable for pump truck inhibitor. The overall mix temperature was56 C. A use where the thickening time is limited. More imsmall amount ofcoarsealuminum was used'along with portant even than this, is the factthat starch-thickened the fine aluminum and proportions of both werevaried slu-rries, particularly of the type under consideration here,slightly as indicated. It will be noted that at the higher require lesssensitizer for a given sensitization, i.e., less temperature indicatedthe products were not generally cap aluminum can be used than when guargum is used as 4 sensitive, although some reaction was indicated incertain thlckener. A series of tests were made which showed instances.At the lower temperature, detonation was that so fas as sensitivity isconcerned, 0.25% of fine slightly better with the potato starchcomposition, despite aluminum combined with a potato starch thickenerwas the fact that less of the fine aluminum was used than in aseifectlve as 0.6% of the same aluminum, using guar most of the othersamples. Compare, for example, Mix

gum as thickener. This result is amplified further by the No. 1 with MixNo. 15, or Mix No. 7 with Mix No. 9.

The importance of particular aluminum qualities is emphasized in acopending application of Clay et al., Serial No. 460,857 filed June 2,1965. The advantages of such compositions are considerably enhanced bythe use of a combination of sulfur and sodium nitrate within particularratio limits, according to the present invention.

There appears to be some uncertainty whether sodium sulfate is animportant heat-producing reaction product. There is reason to believethat the exothermic reaction between sulfur and sodium nitrate mayproduce sodium sulfite and/or sodium sulfide. In any case, it appears tobe clearly established .that the heat of the sodium nitratesulfurreaction is highly important. This is particularly true 'where verysmall quantities of aluminum are employed as the primary or conventionalsensitizer. As noted above, by the use of starch in lieu of gum, or evenin lieu of part of the gum, as a thickener, under favorable conditionsthe sensitizing quantities of aluminum required can be reduced evenfurther.

In summary, the present invention is characterized in one respect by theuse of very small quantities of finely divided metal, preferablyaluminum, which aluminium is of a character suitable to establish manytiny voids as reaction centers. The more reaction centers :present, themore sensitive is the slurry. Because of the high heat of formation ofaluminum oxide, these centers are highly 'efiicient as reactioninitiators, and high temperatures are quickly established at thereaction centers. Moreover, the sodium nitrate-sulfur reaction, whichpossibly involves formations of sodium sulfate and/or sodium sulfite,and/or possibly some sulfide compounds, apparently helps provide theenergy needed to drive the detonation wave thought the column ofexplosive.

In general, the compositions will include at leastv 45% of theoxygen-supplying salt and usually more than 50%, preferably 60% or more.Water may comprise from to 25%, or more in some cases. Sulfur may befrom 1 to 15% and only enough sodium nitrate is used to keep the SN/Sratio below about 2 but above about 0.8. However, it is preferable touse at least 5.0% of sodium nitrate, and the appropriate amount ofsulfur.

The liquid is preferably water, but it maycomprise variouswater-compatible materials,- especially organic liquids having fuelvalue, such as formamide and other amides, alcohols and polyols. Thealuminum or other metal particles should be of such a character as toform reactive sites by retaining very small or tiny pockets or bubblesof gas to cause the reaction. Where temperature of mixing, etc.,permits, it is preferred to use starch as a thickener. These variousfeatures are contemplated individually as well as collectively, asaspects of the invention.

The discovery that highly effective and sensitive ex- Q plosives basedmainly on ammonium nitrate in water can be prepared by the use of verysmall quantities of reactive aluminum having reaction site potentials,and that the power and sensitivity of such aluminum can be furtherenhanced by use of sodium nitrate and sulfur in optimum proportions isconsidered highly significant and technically and economicallyimportant. The further consideration that starch can be used to addfurther control over sensitivity under certain conditions is important,too. It is obvious that numerous variations can be made in thecomposition without departing from the spirit and purpose of theinvention which comprehends all these factors individually and incombination. It is intended by the claims which follow to cover such asfully as the prior art properly permits.

What is claimed is: p

1. An explosive composition comprising at least 45% by weight of oxygensupplying salts, at least half of such salts being ammonium nitrate andat least 5% being'sodium nitrate, the remainder being selected from agroup which consists of ammonium nitrate, alkali metal nitrate, alkalinearth metal nitrates, and the chlorates and perchlorates of ammonia andof the alkali metals, an amount of sulfur to make a weight ratio withthe sodium nitrate between 0.8 and 3.0 SN/S, 0.1 to 8% of particulatemetal selected from the group which consists of aluminum, magnesium,boron, and mixtures thereof, a sufficient quantity of Water to form apourable slurry or gel, and 0.1 to 4% of a thickening agent to inhibitgravity separation of undissolved components of said slurry.

2. Composition according to claim 1 wherein the oxygen supplying saltsconsist of ammonium nitrate and sodium nitrate.

3. Composition according to claim 1 wherein the thickener is starch.

4. Composition according to claim 1 wherein the metal is finely dividedparticulate metal used in proportions not to exceed 2% by weight basedon the total composition.

5. A slurry explosive comprising, in combination, a liquid solution of apowerful oxidizer selected from the group which consists of ammoniumnitrate, sodium nitrate, and the chlorates and perchlorates of ammoniaand the alkali metals, and mixtures of any two or more of these, atleast 1% of sulfur by weight, based on the total composition, a finelydivided particulate metal sensitizer in small proportions, and sodiumnitrate (included in the oxidizer) in such proportions as to make aweight ratio with the sulfur between about 3 :1 and 9.8: 1. i

6. Composition according to claim 5 wherein the metal is aluminum.

7. Composition according to claim 5 wherein a major tion, of a powerfuloxidizer a major part of which is ammonium nitrate, a metallicsensitizer, and at least 5% of sodium nitrate, and enough sulfur toproduceia sodium nitrate/sulfur weight ratio between about 3.0 and 0.8.

13. Composition according to claim 12 wherein the metallic sensitizer isaluminum which has active thermal sites due to occlusion of tiny bubblesof gas.

14. Composition according to claim 12 wherein there is included athickener to inhibit gravity separation of undissolved components.

15. An aqueous explosive slurry composition comprising a majorproportion of solution of ammonium nitrate and sodium nitrate in water,0.1 to 8% of suspended particles of a sensitizing metal having surfaceproperties such as to hold small bubbles of gas while in the slurry,enough sulfur in suspension to make a weight ratio of sodium nitrate tosulfur between about 3.0 and 0.8, and 0.1 to about 4% of a thickener.

16. Composition according to claim 15 wherein the ratio is about 1.

17. Composition according to claim 15 wherein the metal is aluminum inproportions of 1 to 3%.

References Cited by the Examiner UNITED STATES PATENTS 3,092,528 6/ 1963Loving 14973 X 3,113,059 12/1963 Ursenbach et al l49-41 3,249,477 5/1966Clay et a1. 14941 L. DEWAYNE RUTLEDGE, Primary Examiner.

S. I. LECHERT, 111., Assistant Examiner.

1. AN EXPLOSIVE COMPOSITION COMPRISING AT LEAST 45% BY WEIGHT OF OXYGENSUPPLYING SALTS, AT LEAST HALF OF SUCH SALTS BEING AMMONIUM NITRATE ANDAT LEAST 5% BEING SODIUM NITRATE, THE REMAINDER BEING SELECTED FROM AGROUP WHICH CONSISTS OF AMMONIUM NITRATE, ALKALI METAL NITRATE, ALKALINEEARTH METAL NITRATES, AND THE CHLORATES AND PERCHLORATES OF AMMONIA ANDOF THE ALKALI METALS, AN AMOUNT OF SULFUR TO MAKE A WEIGHT RATIO WITHTHE SODIUM NITRATE BETWEEN 0.8 AND 3.0 SN/S, TO 8% OF PARTICULATE METALSELECTED FROM THE GROUP WHICH CONSISTS OF ALUMINUM, MAGNESIUM, BORON,AND MIXTURES THEREOF, A SUFFICIENT QUANTITY OF WATER TO FORM A POURABLESLURRY OR GEL, AND 0.1 TO 4% OF A THICKENING AGENT TO INHIBIT GRAVITYSEPARATION OF UNDISSOLVED COMPONENTS OF SAID SLURRY.